Ancillary Services in Hybrid AC/DC Low Voltage Distribution Networks

In the last decade, distribution systems are experiencing a drastic transformation with the advent of new technologies. In fact, distribution networks are no longer passive systems, considering the current integration rates of new agents such as distributed generation, electrical vehicles and energy storage, which are greatly influencing the way these systems are operated. In addition, the intrinsic DC nature of these components, interfaced to the AC system through power electronics converters, is unlocking the possibility for new distribution topologies based on AC/DC networks. This paper analyzes the evolution of AC distribution systems, the advantages of AC/DC hybrid arrangements and the active role that the new distributed agents may play in the upcoming decarbonized paradigm by providing different ancillary services.Ministerio de Economía y Competitividad ENE2017-84813-RUnión Europea (Programa Horizonte 2020) 76409

Thermoeconomic analysis of residential rooftop photovoltaic systems with integrated energy storage and resulting impacts on electrical distribution networks

journal articleThis paper investigates residential rooftop photovoltaic (PV) systems for long-term thermoeconomic benefits from PV homeowners' perspectives and for impacts on the electrical distribution network from grid operators' perspectives. The costs of generating electricity from grid-connected PV systems are studied with and without energy storage at the PV homeowners' sites. Three selling scenarios for excess PV energy conversion are considered: net metering, wholesale pricing, and no payback. PV systems in Utah are utilized as case studies in this analysis. The presence of PV systems gives homeowners economic benefits such as reduced annual electricity bills. However, the levelized costs of electricity are considerably higher than the weighted electricity price in Utah. Currently, the addition of energy storage only benefits customers in Utah under the no payback policy. The impacts of PV systems toward electrical distribution networks are then studied on a distribution test system. Excess PV generation from residential PV systems causes voltage rise in the electrical distribution network. The results from this paper can educate consumers about the lifetime benefit of integrating solar energy into their homes. For grid operators, residential PV systems with energy storage can reduce the negative impacts on the grid compared with high PV penetration alone

Energy optimization of a concentrated solar power plant with thermal storage

One of the most relevant problems to solve at a planetary scale is the access to an affordable clean source of energy as CO2 equivalent emissions should be reduced significantly. Some authors aim for a zero emissions target for 2050. Renewable energies will play a leading role in this energy transition, and solar energy with storage is a promising technology exploring a renewable and worldwide available resource. Within the present thesis component development like a new thermal storage thermocline tank design or having latent heat storage capability are technological developments that have been pursued and analyzed on a system perspective basis, focusing on reducing the LCOE value of a commercial STE plant using TRNSYS software. Material research with molten salts mixtures and cement based materials has been performed at lab scale. A fully validation should occur through a 13 partners pan-European H2020 project called NEWSOL which has been developed supported on the laboratory data obtained. Moreover, incorporation of local available material, “modern slag” from an old mine of Alentejo region, was also studied. The material could be used as an aggregate incorporated into calcium aluminate cement (CAC) or as filler. This would help to solve a local environmental complex problem related to soil, air and water pollution due to heavy metals and mining activity in Mina de São Domingos, Southeast of Portugal. The integration of these results underlies a broad energy transition model, a proposal is presented in this thesis, with the aim to foster development towards a sustainable usage of resources and promote clean technologies especially in the energy sector. This model can be locally adapted depending on the pattern of existing industries. The goal is to achieve a smooth transition into a clean tech energy society in line with the target of achieving zero emissions for 2050; Optimização Energética de uma Central de Concentração Solar com Armazenamento de Energia Resumo: Um dos problemas mais relevantes a resolver a uma escala planetária é o acesso, com um custo moderado, a fontes limpas de energia considerando que as emissões equivalentes de CO2 derão ser reduzidas drasticamente. Alguns autores ambicionam mesmo um objetivo de zero emissões em 2050. As energias renováveis irão desempenhar um papel preponderante nesta transição energética, sendo que a energia solar com armazenamento é uma tecnologia promissora que aproveita um recurso renovável e disponível em boa parte do Planeta. Na presente tese foi realizado o desenvolvimento de componentes nomeadamente o design que um novo tanque do tipo termocline, ou de novos elementos recorrendo ao calor latente, desenvolvimentos tecnológicos que foram analizados de uma perspectiva de sistema, dando o enfoque na redução do custo nivelado da electricidade (LCOE) para uma planta Termosolar usando o software TRNSYS. Foi também realizada investigação em laboratório ao nível dos materiais com várias misturas de sais fundidos inclusivé em contacto directo com materiais de base cimenticia. Uma validação completa deverá ocorrer no projeto NEWSOL do programa H2020 que reúne um consórcio de 13 parceiros europeus e que foi preparado e submetido tendo por base os resultados laboratoriais obtidos. Adicionalmente, incorporação de material disponível (escória de minério) de uma mina abandonada da região do Alentejo foi outro dos aspectos estudados. Verificou-se que este material poderá ser utilizado como agregado num ligante do tipo cimento de aluminato de cálcio (CAC) ou como “filler”. Este re-aproveitamento resolveria um problema ambiental complexo derivado do elevado conteúdo de metais pesados resultantes da actividade de mineração e que actualamente provocam poluição do solo, água e ar na área da Mina de São Domingos, Sudeste de Portugal. Estes progressos deverão ser integrados num modelo de transição energética mais amplo. Na presente tese, uma proposta concreta é apresentada, com o objectivo de incentivar o desenvolvimento na direção de uma utilização sustentável dos recursos e a promoção de tecnologias limpas nomeadamente no sector da energia. Este modelo poderá ser adaptado localmente dependendo do padrão de indústrias existente. O objectivo é atingir uma transição suave para uma sociedade de energias limpas em linha com o objectivo de atingir zero emissões de CO2 equivalente em 2050

Modelling, thermoeconomic analysis and optimization of hybrid solar-biomass organic Rankine cycle power plants

The need for modern energy systems to embrace the requirements of energy security, sustainability and affordability in their designs has placed emphatic importance on exploitation of renewable resources, such as solar and wind energy, etc. However, these resources often lead to reduced reliability and dispatchability of energy systems; less-efficient conversion processes; high cost of power production; etc. One promising way to ameliorate these challenges is through hybridization of renewable energy resources, and by using organic Rankine cycle (ORC) for power generation. Thus, this PhD research project is aimed at conceptual design and techno-economic optimization of hybrid solar-biomass ORC power plants. The methodologies adopted are in four distinct phases: - First, novel hybrid concentrated solar power (CSP)-biomass scheme was conceived that could function as retrofit to existing CSP-ORC plants as well as in new hybrid plant designs. Thermodynamic models were developed for each plant sub-unit, and yearly techno-economic performance was assessed for the entire system. Specifically, the ORC was modelled based on characteristics of an existing CSP-ORC plant, which currently operates at Ottana, Italy. Off-design models of ORC components were integrated, and their performance was validated using experimental data obtained from the aforementioned real plant. - Second, detailed exergy and exergoeconomic analyses were performed on the proposed hybrid plant, in order to examine the system components with remarkable optimization potentials. The evaluation on optimization potentials considered intrinsic irreversibilities in the respective components, which are imposed by assumptions of systemic and economic constraints. This has been termed enhanced exergy and enhanced exergoeconomic analyses here. - Third, the techno-economic implications of using siloxane mixtures as ORC working fluid were investigated, with the aim of improving heat transfer processes in the ORC plant. The studied fluid pairs were actively selected to satisfy classical thermodynamic requirements, based on established criteria. - Fourth, the biomass retrofit system was optimized multi-objectively, to minimize biomass consumption rate (maximize exergetic efficiency) and to minimize exergy cost rate. Non-dominated Sorting Genetic Algorithm (NSGA-II) was adopted for multi-objective optimization. The conceptual scheme involves parallel hybridization of CSP and biomass systems, such that each is capable of feeding the ORC directly. Results showed that the proposed biomass hybridization concept would increase both thermodynamic efficiency and economic performance of CSP-ORC plants, thereby improving their market competitiveness. Total exergy destroyed and exergy efficiency were quantified for each component, and for the whole system. Overall system exergetic efficiency of about 7 % was obtained. Similarly, exergoeconomic factor was obtained for each system component, and their implications were analysed to identify system components with high potentials for optimization. Furthermore, it was observed that thermodynamic performance of the hybrid plant would be optimized by using siloxane mixtures as ORC working fluid. However, this would result in larger heat exchange surface area, with its attendant cost implications. Lastly, biomass combustion and furnace parameters were obtained, which would simultaneously optimize exergetic efficiency and exergy cost rate for the hybrid plant. In sum, a novel scheme has been developed for hybridizing solar and biomass energy for ORC plants, with huge potentials to improve techno-economic competitiveness of solar-ORC systems

A Systematic Literature Review of the Solar Photovoltaic Value Chain for a Circular Economy

As the solar photovoltaic market booms, so will the volume of photovoltaic (PV) systems entering the waste stream. The same is forecast for lithium-ion batteries from electric vehicles, which at the end of their automotive life can be given a second life by serving as stationary energy storage units for renewable energy sources, including solar PV. The main objective of this paper is to systematically review the “state-of-the-art” research on the solar PV value chain (i.e., from product design to product end-of-life), including its main stages, processes, and stakeholder relationships, in order to identify areas along the value chain where circular strategies could be implemented, thereby advancing the transition of the PV industry towards circularity. To achieve this goal, we conducted a systematic literature review of 148 peer-reviewed articles, published in English between 2000 and 2020. Results show the PV value chain has been studied from a forward flow supply chain perspective and mostly from a technological point of view, with little regard for circular design, circular business models, and PV reuse. This article thus takes an integrated value chain perspective, introduces some of the barriers to circularity that industry players face, and argues that these barriers represent future opportunities for incumbent and new entrants to innovate within a circular PV industry

Optymalizacja procesów transferu energii i transferu elektronowego w biofotowoltaicznych nanourządzeniach zawierających fotosystem I oraz cytochrom c553 z ekstremofilnego krasnorostu Cyanidioschyzon merolae

One of the biggest challenges of modern-day solar technologies is to develop carbon-neutral, efficient and sustainable systems for solar energy conversion into electricity and fuel. Over the last two decades there has been a growing impact of ‘green’ solar conversion technologies based on the natural solar energy converters, such as the robust extremophilic photosystem I (PSI) and its associated protein cofactors. The main bottleneck of the currently available biophotovoltaic and solar-to-fuel technologies is the low power conversion efficiency of the available devices due to wasteful charge recombination reactions at the interfaces between the working modules, as well as instability of the organic and inorganic components. This thesis describes the development of three novel approaches to improve energy and electron transfer in PSI-based biophotoelectrodes and plasmonic nanostructures: (1) construction of all-solid-state mediatorless biophotovoltaic devices incorporating p-doped silicon substrate, extremophilic robust PSI complex and its associated light harvesting antenna (PSI-LHCI) in conjunction with its natural electron donor cytochrome c553 (cyt c553) from a red microalga Cyanidioschyzon merolae and (2), biofunctionalization of the silver nanowires (AgNWs) with a highly organised architecture of the cyt c553/PSI-LHCI assembly for the significant improvement of absorption cross-section of the C. merolae PSI-LHCI complex due to plasmonic interactions between the distinct subpool of chlorophylls (Chls) and AgNWs nanoconstructs. The third (3) approach was based on development of the photo-driven in vitro hydrogen production system following hybridisation of the robust extremophilic PSI-LHCI complex with the novel and established proton reducing catalysts (PRC). The last approach has led to generation of molecular hydrogen with TOF of 521 mol H2 (mol PSI)-1 min-1 and 729 mol H2 (mol PSI)-1 min-1 for the hybrid systems of PSI-LHCI with cobaloxime and the DuBois-type mononuclear nickel proton reduction catalysts, respectively. The TOF values for biophotocatalytic H2 production obtained in this study were 3-fold and 16.6-fold higher than those published for cyanobacterial PSI/PRC hybrid systems employing cobaloxime and a similar Ni mononuclear PRC, respectively. Construction of all-solid-state mediatorless PSI-based nanodevices was facilitated by biopassivation of the p-doped Si substrate with His6-tagged cyt c553, as evidenced by significant lowering of the inherent dark saturation current (J0), a well-known semiconductor surface recombination parameter. Five distinct variants of cyt c553 were obtained by genetically engineering the specific linker peptides of 0-19 amino acids in length between the cyt c553 holoprotein and a C-terminal His6-tag, the latter being the affinity ‘anchor’ used for specific immobilisation of this protein on the semiconductor surface. The calculated 2D Gibbs free energy maps for all the five cyt c553 variants and the protein lacking any peptide linker showed a much higher number of thermodynamically feasible conformations for the cyt c variants containing longer linker peptides upon their specific immobilisation on the Si surface. The bioinformatic calculations were verified by constructing the respective cyt c553/Si bioelectrodes and measuring their dark current-voltage (J-V) characteristics to determine the degree of p-doped Si surface passivation, measured by minimisation of the J0 recombination parameter. The combined bioinformatic and J-V analyses indicated that the cyt c553 variants with longer linker peptides, up to 19AA in length, allowed for more structural flexibility of immobilised cyt c553 in terms of both, orientation and distance of the haem group with respect to the Si surface, resulting in efficient biopassivation of this semiconductor substrate. This molecular approach has allowed for the developing of an alternative, cheap and facile route for significant reduction of the inherent minority charge recombination at the p-doped Si surface. To improve direct electron transfer within all-solid state PSI-based nanodevices, the specific His6-tagged cyt c553 variants, generated in this study, were attached to the Ni-NTA-functionalised p-doped Si surface prior to incorporation of the PSI-LHCI photoactive layer. Such nanoarchitecture resulted in an open-circuit potential increment of 333 μV for the specific PSI-LHCI/cyt c553/Si nanodevice compared to the control device devoid of cyt c553. Moreover, the all-solid state mediatorless PSI-LHCI-based devices produced photocurrents in the range of 104-234 μA/cm2 when a bias of -0.25 V was applied, demonstrating one of the highest photocurrents for this type of solid-state devices reported to date. The power conversion efficiency of the PSI-LHCI/p-doped Si devices was 20-fold higher when 19AA variant of cyt c553 was incorporated as the biological conductive interface between the PSI-LHCI photoactive module and the substrate, demonstrating the significant role of this cyt variant for improving direct electron transfer within the PSI-based all-solid-state mediatorless biophotovoltaic device. In a complementary line of research, it was demonstrated that the highly controlled assembly of C. merolae PSI-LHCI complex on plasmon-generating AgNWs substantially improved the optical functionality of such a novel biohybrid nanostructure. By comparing fluorescence intensities measured for PSI-LHCI complex randomly oriented on AgNWs and the results obtained for the PSI-LHCI/cyt c553 bioconjugate with AgNWs it was concluded that the specific binding of PSI-LHCI complex with the defined uniform orientation yields selective excitation of a pool of Chls that are otherwise almost non-absorbing. This is remarkable, as this work shows for the first time that plasmonic excitations in metallic nanostructures not only can be used to enhance native absorption of photosynthetic pigments, but also, by employing cyt c553 as the conjugation cofactor, to activate the specific Chl pools as the absorbing sites, only when the uniform and well-defined orientation of PSI-LHCI complex with respect to plasmonic nanostructures is achieved. This innovative approach paves the way for the next generation solar energy-converting technologies to outperform the reported-to-date biohybrid devices with respect to power conversion efficiency.Jednym z głównych wyzwań technologicznych jest opracowanie wydajnych i odnawialnych systemów konwersji energii słonecznej w elektryczność i paliwo, stosując zerowy bilans emisji związków węgla. W ciągu ostatnich dwóch dekad nastąpił znaczący postęp w zastosowaniu “zielonych” technologii biofotowoltaicznych, opartych na naturalnych białkach absorbujących energię słoneczną, takich jak fotosystem I (PSI) wraz ze związanymi z nim kompleksami antenowymi i kofaktorami transportu elektronowego. Głównym ograniczeniem obecnych urządzeń fotowoltaicznych jest ich niska wydajność kwantowa, związana z procesami rekombinacji ładunku w interfejsach pomiędzy modułami tych urządzeń, jak również ograniczona stabilność zastosowanych jak dotąd biologicznych i syntetycznych komponentów. W ramach niniejszej rozprawy doktorskiej opracowano nowatorską technologię, polegającą na zastosowaniu wysokostabilnego PSI oraz naturalnego donora elektronów dla tego kompleksu, cytochromu c553 (cyt c553), wyizolowanych z ekstremofilnego krasnorostu Cyanidioschyzon merolae, do konstrukcji trzech typów nanourządzeń biofotowoltaicznych: (1), biofotoogniw w stałej konfiguracji (ang., all-solid-state), zawierających domieszkowany pozytywnie półprzewodnikowy substrat krzemowy (ang., p-doped Si, p-Si) wraz z warstwami fotoaktywnego kompleksu PSI i cyt c553; (2), plazmonowych srebrnych bionanodrutów (AgNWs), funkcjonalizowanych wysokouporządkowaną nanoarchitekturą monowarstw PSI i cyt c553, oraz (3), systemu fotokatalitycznej produkcji wodoru cząsteczkowego in vitro z zastosowaniem kompleksów hybrydowych PSI wraz z syntetycznymi katalizatorami redukcji protonów (ang., proton reducing catalysts, PRC). W przypadku ostatniego z powyższych systemów, optymalizacja biofotokatalitycznej produkcji wodoru cząsteczkowego z zastosowaniem systemów hybrydowych z PSI i PRC, opartych na kobaloksymie i niklowym katalizatorze mononuklearnym typu DuBois, precypitowanych na powierzchni PSI w roztworze wodnym, pozwoliła na osiągnięcie aktywności wydzielania wodoru odpowiednio, 521 moli H2 (mol PSI)-1 min-1 oraz 729 moli H2 (mol PSI)-1 min-1, przewyższając tym samym 3-17-krotnie aktywność wydzielania wodoru w podobnych systemach biohybrydowych i warunkach pomiarowych. Poraz pierwszy zastosowano cyt c553 z C-terminalną metką His6 do biopasywacji półprzewodnikowego substratu p-Si, mierzonej minimalizacją parametru rekombinacji powierzchniowej J0. Poprzez inżynierię genetyczną sklonowano i wyrażono w E. coli 5 różnych wariantów cyt c553, z których 4 zawierały w swej strukturze sekwencje peptydowe o długości 5-19 aminokwasów (AA), aby zbadać ich wpływ na procesy rekombinacji ładunku w obrębie elektrody krzemowej. Peptydy te zostały wstawione pomiędzy holobiałkiem a metką His6, którą zastosowano do unieruchomienia każdego z wariantów cyt c553 na powierzchni elektrody. Obliczenie energii swobodnej Gibbsa pozwoliło na utworzenie konformacyjnych map 2D dla każdego z wariantów, w których pokazano, iż warianty z semi-helikalnym peptydem 19AA przyjmują znacząco większą liczbę termodynamicznie możliwych konformacji na powierzchni elektrody pod względem odległości i kąta nachylenia grupy hemowej w stosunku do powierzchni elektrody. Bioinformatyczna analiza została potwierdzona poprzez ciemniową charakterystykę prądowo-napięciową (J-V) utworzonych odpowiednio bioelektrod krzemowo-cytochromowych. Stwierdzono, że warianty cyt c553 z dłuższymi peptydami pomiędzy metką His6 a holobiałkiem efektywnie minimalizują prądy ciemniowe krzemowego substratu, najprawdopodobniej dzięki istnieniu większej ilości termodynamicznie zoptymalizowanych konformacji cytochromu, pozwalających na minimalizację rekombinacji ładunku powierzchniowego substratu. Funkcjonalizacja elektrody p-Si wariantem cyt c553, charakteryzującym się największym stopniem swobody orientacji grupy hemowej w stosunku powierzchni elektrody krzemowej, pozwoliła na efektywną biopasywację tego półprzewodnikowego substratu poprzez minimalizację parametru J0, co z kolei pozwoliło na zwiększenie parametru Voc o 333 μV w biofotoogniwach typu PSI/cyt c553/p-Si, w porównaniu do kontroli zawierającej jedynie PSI/p-Si. Uzyskano fotoprądy w stałych biofotoogniwach PSI/p-Si w zakresie 104-234 μA cm-2 (przy nadpotencjale -0.25 V), co należy do jednych z najwyższych wartości fotoprądów wygenerowanych przez stałe biofotoogniwa z PSI, w podobnych warunkach pomiarowych. Jednocześnie wydajność konwersji energii słonecznej w fotoogniwach typu PSI-LHCI/cyt c553/p-Si była 20-krotnie wyższa, w obecności wariantu cyt c553 19AA, zastosowanego w tych urządzeniech jako biologiczna warstwa biopasywacji substratu krzemowego oraz warstwa kondukcyjna pomiędzy substratem a PSI. Tym samym wykazano, że ów wariant może być zastosowany w urządzeniach biofotowoltaicznych do zwiększenia transferu elektronowego pomiędzy substratem a PSI. W równoległym i komplementarnym kierunku badań, zastosowanie równomiernej i specyficznie ukierunkowanej nanoarchitektury fotoaktywnej warstwy PSI na plazmonowych nanostrukturach metalicznych AgNWs, sfunkcjonalizowanych uprzednio cyt c553, pozwoliło na znaczące zwiększenie efektywnej absorpcji PSI, w zakresie spektralnym, w którym PSI jest nieaktywny in vivo, poprzez aktywację specyficznej puli tzw. czerwonych cząsteczek chlorofilu w obrębie fluoroforów PSI. Tym samym pokazano, że oddziaływania plazmonowe mogą być efektywnie zastosowane nie tylko do zwiększenia całkowitej absorpcji fotoaktywnych kompleksów białkowych, ale również do aktywacji spektralnej specyficznych pigmentów, wyłącznie w obrębie wysokouporządkowanej i zorientowanej nanoarchitektury tych fotokompleksów na nanokonstruktach plazmonowych. Powyższe nowatorskie podejście badawcze może być w przyszłości zastosowane do konstrukcji nowej generacji urządzeń biofotowoltaicznych o zwiększonej wydajności konwersji energii słonecznej

Innovative Nanomaterial Approaches For Solar Energy Applications

The fundamental limitation of the conversion efficiency achievable with solar energy solutions (which includes photovoltaic and photothermal technology), requires the adaptation and integration of a series of innovative material strategies to continue the process of sustainably decarbonizing the global economy. Through the passive integration of additional nanoscale features which exploit and modify the solar spectrum through its interactions with luminescent molecules, metal nanoparticles, and/or thin-film optical coatings – the solar spectrum can be modulated and accordingly the collection efficiency of each respective technology enhanced. However, irrespective of the type of spectral conversion integrated into the technology (luminescent down-shifting, nanofluids, plasmonic luminescent down-shifting, or spectral beam splitting), a series of additional loss mechanisms are introduced as a result of the architectural modifications. Through a proposed series of innovative & iterative advancements in each one of these material strategies, the objective of alleviating the additional loss mechanisms through a suitable combination of the individual approaches could potentially be realised

Techno-Economic Evaluation of Long-Term Energy Storage Options for Variable Renewable Energies in South Africa.

Mechanical and Mechatronic Engineerin